1. Field of the Invention
This invention relates to an image forming apparatus such as a copying apparatus, a laser printer or a facsimile apparatus, a process cartridge detachably attachable on the image forming apparatus, and a cleaning member for cleaning an image bearing member.
Particularly, the present invention relates to a cleaning member for cleaning the surface of an image bearing member, an image forming apparatus provided with the cleaning member, and process cartridge.
2. Related Background Art
FIG. 5 of the accompanying drawings schematically shows the construction of an image forming apparatus such as a copying apparatus or a laser printer. In FIG. 5, the letter M designates the main body of the image forming apparatus as a printer engine. The reference numeral 1 denotes a cylindrical photosensitive drum as an image bearing member rotatively driven in the direction of arrow R1 by driving means (not shown). The surface of the photosensitive drum 1 is uniformly charged by a charging device 2 disposed in contact therewith to form a charging nip portion N.sub.1 and is rotated in the direction of arrow R2, whereafter an electrostatic latent image is formed thereon by an exposing device 3. A developing device (toner image forming means) is provided with a hopper, which is a toner containing device, for effecting the storage and custody of a toner T, and a developing sleeve 4a, which is a toner bearing member, and develops the electrostatic latent image formed on the photosensitive drum 1. A developing blade 4b, which is a toner regulating member, is installed near the developing sleeve 4a rotated in the direction of arrow R4. A developing bias, comprising an AC bias superposed on a DC bias, is supplied between the photosensitive drum 1 and the developing sleeve 4a by an engine control portion 8 provided with a power source for driving the image forming apparatus and a high voltage circuit for supplying a bias for forming an image, whereby the toner adheres to the electrostatic latent image on the photosensitive drum 1 and the latent image is developed as a toner image. The toner image on the photosensitive drum 1 is transferred to a transfer material P, such as paper, by a transferring device (transferring means) 5 rotated in the direction of arrow R5. The transfer material P is kept in a sheet feeding cassette (not shown), and is fed by a sheet feeding roller (not shown) and is sent to the transfer nip portion N.sub.2 between the photosensitive drum 1 and the transferring device 5 in synchronism with the toner image on the photosensitive drum 1 by registration rollers 9. The toner image transferred to the transfer material P is conveyed to a fixing device 7 with the transfer material P, and there it is heated and pressed and thereby fixed on the transfer material P, and becomes a recorded image. On the other hand, any toner remaining on the photosensitive drum 1 without being transferred to the transfer material P after the transfer of the toner image (hereinafter referred to as the "untransferred toner") is removed by a cleaning blade 6a in a cleaning device (cleaning means) 6. The photosensitive drum 1, after the untransferred toner on the surface thereof has been removed, is used for the next cycle of image formation beginning with the charging by the charging device 2, and repeats the above-described series of image forming processes.
Recently, with the spread of computers, electrophotographic recording apparatuses have come to be used as the output apparatuses thereof in various countries of the world. Therefore, it is required that images of high quality be obtained even in an environment of high temperature and high humidity. Also, a variety of transfer materials are used in various countries and therefore, it is desired for an electrographic recording apparatus to be able to be adapted thereto.
At present, as a serious problem in the environment of high temperature and high humidity, there is the problem of a smeared image (smudging). This smeared image may sometimes occur also by dew condensation on the surface of the photosensitive drum, but often occurs because talc, contained in the transfer material, adheres to the surface of the photosensitive drum, oxides due to ozone produced from the charging device, and combines with the moisture from high humidity to create a low resistance substance which disturbs, the latent image. The smeared image may also occur due to the interfacial active agent on the surface of the OHP sheet adhering to the formed image.
As a measure for removing the above-mentioned low resistance substance, it is conceived to reduce the molecular weight of binding resin on the surface layer of the photosensitive drum, and increase the amount of friction during cleaning. However, if the molecular weight of the binding resin is reduced, the surface of the photosensitive drum becomes liable to be roughened when it is frictionally contacted, and this leads to poor cleaning in which, particularly at a low temperatures, the toner rubs through with the hardened cleaning blade, thereby rendering it difficult for the prevention of a smeared image to be compatible with cleaning at a low temperatures.
As an image forming apparatus in which the above-described smeared image is prevented, there is an image forming apparatus described, for example, in Japanese Patent Application Laid-Open No. 62-160458. The photosensitive layer of an electrophotographic photosensitive member contains therein at least one kind of polycarbonate resin having a number average molecular weight of 1.5.times.10.sup.4 or less and at least one kind of polycarbonate resin having a number average molecular weight of 4.5.times.10.sup.4 or greater. The polycarbonate resin having a number average molecular weight of 1.5.times.10.sup.4 or less is contained at a rate of 30 to 95 parts by weight in a composition comprising polycarbonate resin having a number average molecular weight of 1.5.times.10.sup.4 or less and polycarbonate resin having a number average molecular weight of 4.5.times.10.sup.4 or greater.
However, even when the construction as described in Japanese Patent Application Laid-Open No. 62-160458 was adopted, the cleaning property like that of the present invention could not be obtained.